I have the original yellow filter but i use a 41-46 step up instead. Reason is the original leitz filter is not a screw in filter, all you do is push it in and rotate to 'lock' it. However it is not really locked , more of just going into a slot. It happened to me couple of times the filter fell loose. So i decided to keep it well in its original box but in the dry cabin.
The 41-46 step up will fit the XOONS hood nicely, so it wont be visible from outside. However, due to its size, will have to remove the stepup ring to unmount the XOONS. Maybe a 41-40.5 adapter will solve the problem. Not an issue to me. Changing of filter is fine.
Hope this helps!